(gss_cred_id_t, modify, optional) Opaque handle
identifying credential to be released. If GSS_C_NO_CREDENTIAL is
supplied, the routine will complete successfully, but will do
Informs GSS-API that the specified credential handle is no longer
required by the application, and frees associated resources. The
cred_handle is set to GSS_C_NO_CREDENTIAL on successful completion
of this call.
`GSS_S_COMPLETE`: Successful completion.
`GSS_S_NO_CRED`: Credentials could not be accessed.